The present invention relates to composite structures. More particularly, the present invention relates to repairing composite structures that have experienced a delamination.
Composite structures are commonly used in, for example, gas turbine engines. Engine manufacturers are continuously developing lighter weight gas turbine engines so as to improve engine operating efficiencies. One of the most effective ways to improve the structural performance of rotating components is to reduce their weight. This results in lower rotational inertia forces, which reduces the internal loads experienced by the components. Thus, light weight composite structures have been adopted within the industry not just for stator components such as vanes and seals, but additionally for rotating structures such as blades.
One composite structure typically used in aerospace and other applications is a composite having a face skin made of laminated plies with a resin matrix. The plies can be of known lightweight materials such as carbon fiber and/or fiberglass. In one embodiment, the face skin, along with a back skin, sandwich a core that is formed of honeycomb or some other lightweight material. The core is inserted between and bonded to the face skin and the back skin.
During operation of the gas turbine engine, the composite structure is subjected to loads and other environmental factors that result from cyclic stresses, impact, elevated temperatures, and other phenomena. The loads are transferred from one layer to the next by shear through the resin matrix or interface of the plies. The interlaminar shear forces, which transfer loads from one ply to the next, can initiate delamination of the composite structure.
Delamination is particularly problematic for rotating composite components as typical repairs such as scarfing, where the delaminated portion of the plies are ground out and replaced with new plies, are not considered structurally adequate to meet impact requirements. As a result, composite components must be scrapped rather than repaired at great cost to airframers.